Wireless communication networks, enabling voice and data communications to wireless devices, are ubiquitous in many parts of the world, and continue to advance in technological sophistication, system capacity, data rates, bandwidth, supported services, and the like. A basic model of one type of wireless network, generally known as “cellular,” features a plurality of generally fixed network nodes (known variously as base station, radio base station, base transceiver station, serving node, NodeB, eNodeB, eNB, gNB, and the like), each providing wireless communication service to a large plurality of wireless devices (known variously as mobile terminals, User Equipment or UE, and the like) within a generally fixed geographical area, known as a cell or sector.
Wireless communications propagate between network nodes, such as a base station and a UE, as information modulated onto radio frequency (RF) carrier signals, which are transmitted by one node across an air interface, and received and demodulated by the other node. Because the medium is necessarily open (as opposed to a copper wire or optical fiber, which can be physically secured), security is a primary concern, and security features are designed into the technical specifications that govern network operation. For example, most user plane signals (those carrying user data, such as voice, video, text, images, and the like) are encrypted. Many control plane signals (those related to technical operation of the network, often referred to as “overhead”) are integrity protected, meaning that the contents are not encrypted; however, cryptographic means ensure the receiving node can unambiguously authenticate the identity of the transmitting node. Both encryption and integrity protection are cryptographic operations which rely on the generation and use of various “keys,” or unique data that are known (or derivable) only by legitimate parties to the communication. Cryptographic operations only work if the different parties use the same, or compatible, keys.
Radio Resource Control States in LTE and NR Radio Resource Control (RRC) is an air interface protocol used in the 3rd generation (3G) mobile cellular wireless network protocol Universal Mobile Telecommunications System (UMTS), as well as the 4th generation (4G) protocol, Long Term Evolution (LTE). Modifications to RRC are proposed for the 5th generation (5G) protocol, New Radio (NR). The Third Generation Partnership Project (3GPP) specifications for UMTS RRC are in Technical Standard (TS) 25.331, and for LTE are in TS 36.331.
In LTE, two general RRC modes are defined for a wireless device, or User Equipment (UE): RRC_IDLE and RRC_CONNECTED. Within the RRC_CONNECTED mode, a UE transitions between further RRC states, each having lower power consumption, based on inactivity timers. The RRC_CONNECTED mode states for LTE are CELL-DCH (Dedicated Channel), CELL_FACH (Forward Access Channel), CELL_PCH (Cell Paging Channel) and URA_PCH (UTRAN Registration Area, or URA, Paging Channel). This disclosure focuses on transitions between RRC_CONNECTED and RRC_IDLE modes (and analogous NR RRC transitions), not the RRC_CONNECTED states. Accordingly, as used herein, the terms RRC mode and RRC state are used interchangeably.
In LTE RRC_IDLE state, a UE is known to the core network (CN or EPC), and has an Internet Protocol (IP) address, but is not known/tracked by the Radio Access Network (E-UTRAN/eNB). The UE can receive broadcast/multicast data (e.g., System Information, or SI); monitors a paging channel to detect incoming calls; may perform neighbor cell measurements; and can do cell (re)selection. A UE in RRC_IDLE may be configured by the network for Discontinuous Reception (DRX).
In the LTE RRC_CONNECTED state, the UE is known by the RAN (E-UTRAN/eNB), as well as the core network, and the mobility of the UE is managed by the network. The UE monitors control channels for downlink data, sends channel quality feedback, and may request uplink resources. The RRC messages RRCRelease and RRCConnect transition the UE from RRC_CONNECTED to and from RRC_INACTIVE states.
In LTE Rel-13 a mechanism was introduced for the UE to be suspended by the network in a suspended state similar to RRC_IDLE but with the difference that the UE stores the Access Stratum (AS) context or RRC context. This makes it possible to reduce the signaling when the UE again becomes active by resuming the RRC connection, instead of (as prior) to establish the RRC connection from scratch. Reducing the signaling could have several benefits. First, it would reduce latency, e.g., for smart phones accessing the Internet. Second, the reduced signaling would reduce battery consumption, which is particularly important for machine type devices sending very little data.
The basis of the Rel-13 solution is that the UE sends a RRCConnectionResumeRequest message to the network, and in response receives an RRCConnectionResume from the network. The RRCConnectionResume is not encrypted but is integrity protected.
As part of the standardized work on 5G NR in 3GPP, it has been decided that NR should support an RRC_INACTIVE state with similar properties as the suspended state in LTE Rel-13. The RRC_INACTIVE has slightly different properties from the LTE Rel-13 suspended state, in that it is a separate RRC state and not part of RRC_IDLE, as in LTE. Additionally, the CN/RAN connection (NG or N2 interface) is kept for RRC_INACTIVE while it was suspended in LTE. FIG. 1 depicts the possible RRC state transitions in NR.
The NR RRC states have the following properties:
RRC_IDLE:
                A UE specific DRX may be configured by upper layers;        UE controlled mobility based on network configuration;        The UE:                    Monitors a Paging channel for CN paging using 5G-S-TMSI;                        Performs neighbouring cell measurements and cell (re-)selection;        Acquires system information.RRC_INACTIVE:        A UE specific DRX may be configured by upper layers or by RRC layer;        UE controlled mobility based on network configuration;        The UE stores the AS context;        The UE:                    Monitors a Paging channel for CN paging using 5G-S-TMSI and RAN paging using I-RNTI;            Performs neighbouring cell measurements and cell (re-)selection;            Performs RAN-based notification area updates periodically and when moving outside the RAN-based notification area;            Acquires system information.RRC_CONNECTED:                        The UE stores the AS context.        Transfer of unicast data to/from UE.        At lower layers, the UE may be configured with a UE specific DRX;        For UEs supporting CA, use of one or more SCells, aggregated with the SpCell, for increased bandwidth;        For UEs supporting DC, use of one SCG, aggregated with the MCG, for increased bandwidth;        Network controlled mobility, i.e. handover within NR and to/from E-UTRAN.        The UE:                    Monitors a Paging channel;            Monitors control channels associated with the shared data channel to determine if data is scheduled for it;            Provides channel quality and feedback information;            Performs neighbouring cell measurements and measurement reporting;            Acquires system information.                        